summaryrefslogtreecommitdiffstats
path: root/fs/btrfs/async-thread.c
blob: 8aec751fa464c126a7fd80e21b526692896d98c9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/freezer.h>
#include "async-thread.h"

#define WORK_QUEUED_BIT 0
#define WORK_DONE_BIT 1
#define WORK_ORDER_DONE_BIT 2
#define WORK_HIGH_PRIO_BIT 3

/*
 * container for the kthread task pointer and the list of pending work
 * One of these is allocated per thread.
 */
struct btrfs_worker_thread {
	/* pool we belong to */
	struct btrfs_workers *workers;

	/* list of struct btrfs_work that are waiting for service */
	struct list_head pending;
	struct list_head prio_pending;

	/* list of worker threads from struct btrfs_workers */
	struct list_head worker_list;

	/* kthread */
	struct task_struct *task;

	/* number of things on the pending list */
	atomic_t num_pending;

	/* reference counter for this struct */
	atomic_t refs;

	unsigned long sequence;

	/* protects the pending list. */
	spinlock_t lock;

	/* set to non-zero when this thread is already awake and kicking */
	int working;

	/* are we currently idle */
	int idle;
};

static int __btrfs_start_workers(struct btrfs_workers *workers);

/*
 * btrfs_start_workers uses kthread_run, which can block waiting for memory
 * for a very long time.  It will actually throttle on page writeback,
 * and so it may not make progress until after our btrfs worker threads
 * process all of the pending work structs in their queue
 *
 * This means we can't use btrfs_start_workers from inside a btrfs worker
 * thread that is used as part of cleaning dirty memory, which pretty much
 * involves all of the worker threads.
 *
 * Instead we have a helper queue who never has more than one thread
 * where we scheduler thread start operations.  This worker_start struct
 * is used to contain the work and hold a pointer to the queue that needs
 * another worker.
 */
struct worker_start {
	struct btrfs_work work;
	struct btrfs_workers *queue;
};

static void start_new_worker_func(struct btrfs_work *work)
{
	struct worker_start *start;
	start = container_of(work, struct worker_start, work);
	__btrfs_start_workers(start->queue);
	kfree(start);
}

/*
 * helper function to move a thread onto the idle list after it
 * has finished some requests.
 */
static void check_idle_worker(struct btrfs_worker_thread *worker)
{
	if (!worker->idle && atomic_read(&worker->num_pending) <
	    worker->workers->idle_thresh / 2) {
		unsigned long flags;
		spin_lock_irqsave(&worker->workers->lock, flags);
		worker->idle = 1;

		/* the list may be empty if the worker is just starting */
		if (!list_empty(&worker->worker_list) &&
		    !worker->workers->stopping) {
			list_move(&worker->worker_list,
				 &worker->workers->idle_list);
		}
		spin_unlock_irqrestore(&worker->workers->lock, flags);
	}
}

/*
 * helper function to move a thread off the idle list after new
 * pending work is added.
 */
static void check_busy_worker(struct btrfs_worker_thread *worker)
{
	if (worker->idle && atomic_read(&worker->num_pending) >=
	    worker->workers->idle_thresh) {
		unsigned long flags;
		spin_lock_irqsave(&worker->workers->lock, flags);
		worker->idle = 0;

		if (!list_empty(&worker->worker_list) &&
		    !worker->workers->stopping) {
			list_move_tail(&worker->worker_list,
				      &worker->workers->worker_list);
		}
		spin_unlock_irqrestore(&worker->workers->lock, flags);
	}
}

static void check_pending_worker_creates(struct btrfs_worker_thread *worker)
{
	struct btrfs_workers *workers = worker->workers;
	struct worker_start *start;
	unsigned long flags;

	rmb();
	if (!workers->atomic_start_pending)
		return;

	start = kzalloc(sizeof(*start), GFP_NOFS);
	if (!start)
		return;

	start->work.func = start_new_worker_func;
	start->queue = workers;

	spin_lock_irqsave(&workers->lock, flags);
	if (!workers->atomic_start_pending)
		goto out;

	workers->atomic_start_pending = 0;
	if (workers->num_workers + workers->num_workers_starting >=
	    workers->max_workers)
		goto out;

	workers->num_workers_starting += 1;
	spin_unlock_irqrestore(&workers->lock, flags);
	btrfs_queue_worker(workers->atomic_worker_start, &start->work);
	return;

out:
	kfree(start);
	spin_unlock_irqrestore(&workers->lock, flags);
}

static noinline void run_ordered_completions(struct btrfs_workers *workers,
					    struct btrfs_work *work)
{
	if (!workers->ordered)
		return;

	set_bit(WORK_DONE_BIT, &work->flags);

	spin_lock(&workers->order_lock);

	while (1) {
		if (!list_empty(&workers->prio_order_list)) {
			work = list_entry(workers->prio_order_list.next,
					  struct btrfs_work, order_list);
		} else if (!list_empty(&workers->order_list)) {
			work = list_entry(workers->order_list.next,
					  struct btrfs_work, order_list);
		} else {
			break;
		}
		if (!test_bit(WORK_DONE_BIT, &work->flags))
			break;

		/* we are going to call the ordered done function, but
		 * we leave the work item on the list as a barrier so
		 * that later work items that are done don't have their
		 * functions called before this one returns
		 */
		if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
			break;

		spin_unlock(&workers->order_lock);

		work->ordered_func(work);

		/* now take the lock again and drop our item from the list */
		spin_lock(&workers->order_lock);
		list_del(&work->order_list);
		spin_unlock(&workers->order_lock);

		/*
		 * we don't want to call the ordered free functions
		 * with the lock held though
		 */
		work->ordered_free(work);
		spin_lock(&workers->order_lock);
	}

	spin_unlock(&workers->order_lock);
}

static void put_worker(struct btrfs_worker_thread *worker)
{
	if (atomic_dec_and_test(&worker->refs))
		kfree(worker);
}

static int try_worker_shutdown(struct btrfs_worker_thread *worker)
{
	int freeit = 0;

	spin_lock_irq(&worker->lock);
	spin_lock(&worker->workers->lock);
	if (worker->workers->num_workers > 1 &&
	    worker->idle &&
	    !worker->working &&
	    !list_empty(&worker->worker_list) &&
	    list_empty(&worker->prio_pending) &&
	    list_empty(&worker->pending) &&
	    atomic_read(&worker->num_pending) == 0) {
		freeit = 1;
		list_del_init(&worker->worker_list);
		worker->workers->num_workers--;
	}
	spin_unlock(&worker->workers->lock);
	spin_unlock_irq(&worker->lock);

	if (freeit)
		put_worker(worker);
	return freeit;
}

static struct btrfs_work *get_next_work(struct btrfs_worker_thread *worker,
					struct list_head *prio_head,
					struct list_head *head)
{
	struct btrfs_work *work = NULL;
	struct list_head *cur = NULL;

	if (!list_empty(prio_head))
		cur = prio_head->next;

	smp_mb();
	if (!list_empty(&worker->prio_pending))
		goto refill;

	if (!list_empty(head))
		cur = head->next;

	if (cur)
		goto out;

refill:
	spin_lock_irq(&worker->lock);
	list_splice_tail_init(&worker->prio_pending, prio_head);
	list_splice_tail_init(&worker->pending, head);

	if (!list_empty(prio_head))
		cur = prio_head->next;
	else if (!list_empty(head))
		cur = head->next;
	spin_unlock_irq(&worker->lock);

	if (!cur)
		goto out_fail;

out:
	work = list_entry(cur, struct btrfs_work, list);

out_fail:
	return work;
}

/*
 * main loop for servicing work items
 */
static int worker_loop(void *arg)
{
	struct btrfs_worker_thread *worker = arg;
	struct list_head head;
	struct list_head prio_head;
	struct btrfs_work *work;

	INIT_LIST_HEAD(&head);
	INIT_LIST_HEAD(&prio_head);

	do {
again:
		while (1) {


			work = get_next_work(worker, &prio_head, &head);
			if (!work)
				break;

			list_del(&work->list);
			clear_bit(WORK_QUEUED_BIT, &work->flags);

			work->worker = worker;

			work->func(work);

			atomic_dec(&worker->num_pending);
			/*
			 * unless this is an ordered work queue,
			 * 'work' was probably freed by func above.
			 */
			run_ordered_completions(worker->workers, work);

			check_pending_worker_creates(worker);
			cond_resched();
		}

		spin_lock_irq(&worker->lock);
		check_idle_worker(worker);

		if (freezing(current)) {
			worker->working = 0;
			spin_unlock_irq(&worker->lock);
			try_to_freeze();
		} else {
			spin_unlock_irq(&worker->lock);
			if (!kthread_should_stop()) {
				cpu_relax();
				/*
				 * we've dropped the lock, did someone else
				 * jump_in?
				 */
				smp_mb();
				if (!list_empty(&worker->pending) ||
				    !list_empty(&worker->prio_pending))
					continue;

				/*
				 * this short schedule allows more work to
				 * come in without the queue functions
				 * needing to go through wake_up_process()
				 *
				 * worker->working is still 1, so nobody
				 * is going to try and wake us up
				 */
				schedule_timeout(1);
				smp_mb();
				if (!list_empty(&worker->pending) ||
				    !list_empty(&worker->prio_pending))
					continue;

				if (kthread_should_stop())
					break;

				/* still no more work?, sleep for real */
				spin_lock_irq(&worker->lock);
				set_current_state(TASK_INTERRUPTIBLE);
				if (!list_empty(&worker->pending) ||
				    !list_empty(&worker->prio_pending)) {
					spin_unlock_irq(&worker->lock);
					set_current_state(TASK_RUNNING);
					goto again;
				}

				/*
				 * this makes sure we get a wakeup when someone
				 * adds something new to the queue
				 */
				worker->working = 0;
				spin_unlock_irq(&worker->lock);

				if (!kthread_should_stop()) {
					schedule_timeout(HZ * 120);
					if (!worker->working &&
					    try_worker_shutdown(worker)) {
						return 0;
					}
				}
			}
			__set_current_state(TASK_RUNNING);
		}
	} while (!kthread_should_stop());
	return 0;
}

/*
 * this will wait for all the worker threads to shutdown
 */
void btrfs_stop_workers(struct btrfs_workers *workers)
{
	struct list_head *cur;
	struct btrfs_worker_thread *worker;
	int can_stop;

	spin_lock_irq(&workers->lock);
	workers->stopping = 1;
	list_splice_init(&workers->idle_list, &workers->worker_list);
	while (!list_empty(&workers->worker_list)) {
		cur = workers->worker_list.next;
		worker = list_entry(cur, struct btrfs_worker_thread,
				    worker_list);

		atomic_inc(&worker->refs);
		workers->num_workers -= 1;
		if (!list_empty(&worker->worker_list)) {
			list_del_init(&worker->worker_list);
			put_worker(worker);
			can_stop = 1;
		} else
			can_stop = 0;
		spin_unlock_irq(&workers->lock);
		if (can_stop)
			kthread_stop(worker->task);
		spin_lock_irq(&workers->lock);
		put_worker(worker);
	}
	spin_unlock_irq(&workers->lock);
}

/*
 * simple init on struct btrfs_workers
 */
void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max,
			struct btrfs_workers *async_helper)
{
	workers->num_workers = 0;
	workers->num_workers_starting = 0;
	INIT_LIST_HEAD(&workers->worker_list);
	INIT_LIST_HEAD(&workers->idle_list);
	INIT_LIST_HEAD(&workers->order_list);
	INIT_LIST_HEAD(&workers->prio_order_list);
	spin_lock_init(&workers->lock);
	spin_lock_init(&workers->order_lock);
	workers->max_workers = max;
	workers->idle_thresh = 32;
	workers->name = name;
	workers->ordered = 0;
	workers->atomic_start_pending = 0;
	workers->atomic_worker_start = async_helper;
	workers->stopping = 0;
}

/*
 * starts new worker threads.  This does not enforce the max worker
 * count in case you need to temporarily go past it.
 */
static int __btrfs_start_workers(struct btrfs_workers *workers)
{
	struct btrfs_worker_thread *worker;
	int ret = 0;

	worker = kzalloc(sizeof(*worker), GFP_NOFS);
	if (!worker) {
		ret = -ENOMEM;
		goto fail;
	}

	INIT_LIST_HEAD(&worker->pending);
	INIT_LIST_HEAD(&worker->prio_pending);
	INIT_LIST_HEAD(&worker->worker_list);
	spin_lock_init(&worker->lock);

	atomic_set(&worker->num_pending, 0);
	atomic_set(&worker->refs, 1);
	worker->workers = workers;
	worker->task = kthread_create(worker_loop, worker,
				      "btrfs-%s-%d", workers->name,
				      workers->num_workers + 1);
	if (IS_ERR(worker->task)) {
		ret = PTR_ERR(worker->task);
		goto fail;
	}

	spin_lock_irq(&workers->lock);
	if (workers->stopping) {
		spin_unlock_irq(&workers->lock);
		goto fail_kthread;
	}
	list_add_tail(&worker->worker_list, &workers->idle_list);
	worker->idle = 1;
	workers->num_workers++;
	workers->num_workers_starting--;
	WARN_ON(workers->num_workers_starting < 0);
	spin_unlock_irq(&workers->lock);

	wake_up_process(worker->task);
	return 0;

fail_kthread:
	kthread_stop(worker->task);
fail:
	kfree(worker);
	spin_lock_irq(&workers->lock);
	workers->num_workers_starting--;
	spin_unlock_irq(&workers->lock);
	return ret;
}

int btrfs_start_workers(struct btrfs_workers *workers)
{
	spin_lock_irq(&workers->lock);
	workers->num_workers_starting++;
	spin_unlock_irq(&workers->lock);
	return __btrfs_start_workers(workers);
}

/*
 * run through the list and find a worker thread that doesn't have a lot
 * to do right now.  This can return null if we aren't yet at the thread
 * count limit and all of the threads are busy.
 */
static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
{
	struct btrfs_worker_thread *worker;
	struct list_head *next;
	int enforce_min;

	enforce_min = (workers->num_workers + workers->num_workers_starting) <
		workers->max_workers;

	/*
	 * if we find an idle thread, don't move it to the end of the
	 * idle list.  This improves the chance that the next submission
	 * will reuse the same thread, and maybe catch it while it is still
	 * working
	 */
	if (!list_empty(&workers->idle_list)) {
		next = workers->idle_list.next;
		worker = list_entry(next, struct btrfs_worker_thread,
				    worker_list);
		return worker;
	}
	if (enforce_min || list_empty(&workers->worker_list))
		return NULL;

	/*
	 * if we pick a busy task, move the task to the end of the list.
	 * hopefully this will keep things somewhat evenly balanced.
	 * Do the move in batches based on the sequence number.  This groups
	 * requests submitted at roughly the same time onto the same worker.
	 */
	next = workers->worker_list.next;
	worker = list_entry(next, struct btrfs_worker_thread, worker_list);
	worker->sequence++;

	if (worker->sequence % workers->idle_thresh == 0)
		list_move_tail(next, &workers->worker_list);
	return worker;
}

/*
 * selects a worker thread to take the next job.  This will either find
 * an idle worker, start a new worker up to the max count, or just return
 * one of the existing busy workers.
 */
static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
{
	struct btrfs_worker_thread *worker;
	unsigned long flags;
	struct list_head *fallback;
	int ret;

	spin_lock_irqsave(&workers->lock, flags);
again:
	worker = next_worker(workers);

	if (!worker) {
		if (workers->num_workers + workers->num_workers_starting >=
		    workers->max_workers) {
			goto fallback;
		} else if (workers->atomic_worker_start) {
			workers->atomic_start_pending = 1;
			goto fallback;
		} else {
			workers->num_workers_starting++;
			spin_unlock_irqrestore(&workers->lock, flags);
			/* we're below the limit, start another worker */
			ret = __btrfs_start_workers(workers);
			spin_lock_irqsave(&workers->lock, flags);
			if (ret)
				goto fallback;
			goto again;
		}
	}
	goto found;

fallback:
	fallback = NULL;
	/*
	 * we have failed to find any workers, just
	 * return the first one we can find.
	 */
	if (!list_empty(&workers->worker_list))
		fallback = workers->worker_list.next;
	if (!list_empty(&workers->idle_list))
		fallback = workers->idle_list.next;
	BUG_ON(!fallback);
	worker = list_entry(fallback,
		  struct btrfs_worker_thread, worker_list);
found:
	/*
	 * this makes sure the worker doesn't exit before it is placed
	 * onto a busy/idle list
	 */
	atomic_inc(&worker->num_pending);
	spin_unlock_irqrestore(&workers->lock, flags);
	return worker;
}

/*
 * btrfs_requeue_work just puts the work item back on the tail of the list
 * it was taken from.  It is intended for use with long running work functions
 * that make some progress and want to give the cpu up for others.
 */
void btrfs_requeue_work(struct btrfs_work *work)
{
	struct btrfs_worker_thread *worker = work->worker;
	unsigned long flags;
	int wake = 0;

	if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
		return;

	spin_lock_irqsave(&worker->lock, flags);
	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
		list_add_tail(&work->list, &worker->prio_pending);
	else
		list_add_tail(&work->list, &worker->pending);
	atomic_inc(&worker->num_pending);

	/* by definition we're busy, take ourselves off the idle
	 * list
	 */
	if (worker->idle) {
		spin_lock(&worker->workers->lock);
		worker->idle = 0;
		list_move_tail(&worker->worker_list,
			      &worker->workers->worker_list);
		spin_unlock(&worker->workers->lock);
	}
	if (!worker->working) {
		wake = 1;
		worker->working = 1;
	}

	if (wake)
		wake_up_process(worker->task);
	spin_unlock_irqrestore(&worker->lock, flags);
}

void btrfs_set_work_high_prio(struct btrfs_work *work)
{
	set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
}

/*
 * places a struct btrfs_work into the pending queue of one of the kthreads
 */
void btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
{
	struct btrfs_worker_thread *worker;
	unsigned long flags;
	int wake = 0;

	/* don't requeue something already on a list */
	if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
		return;

	worker = find_worker(workers);
	if (workers->ordered) {
		/*
		 * you're not allowed to do ordered queues from an
		 * interrupt handler
		 */
		spin_lock(&workers->order_lock);
		if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
			list_add_tail(&work->order_list,
				      &workers->prio_order_list);
		} else {
			list_add_tail(&work->order_list, &workers->order_list);
		}
		spin_unlock(&workers->order_lock);
	} else {
		INIT_LIST_HEAD(&work->order_list);
	}

	spin_lock_irqsave(&worker->lock, flags);

	if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
		list_add_tail(&work->list, &worker->prio_pending);
	else
		list_add_tail(&work->list, &worker->pending);
	check_busy_worker(worker);

	/*
	 * avoid calling into wake_up_process if this thread has already
	 * been kicked
	 */
	if (!worker->working)
		wake = 1;
	worker->working = 1;

	if (wake)
		wake_up_process(worker->task);
	spin_unlock_irqrestore(&worker->lock, flags);
}
OpenPOWER on IntegriCloud